MAZAR-I-SHARIF Afghanistan (Reuters) - Two Taliban gunmen in police uniforms attacked the headquarters of police in Afghanistan s major northern city Mazar-i-Sharif on Sunday, killing two and injuring at least 18 others according to local officials.

The insurgents have stepped up attacks on Afghan security forces over the summer fighting season, taking advantage of the withdrawal of foreign troops to regain strategic territory around the country.

Ambitious attacks on security forces are rare in northern Balkh province, where Sunday s incident took place, but in other parts of Afghanistan, insurgents battle the police and army daily.

It was the first such incident in Balkh province, said Abdul Razaq Qaderi the acting police chief of Balkh. Police reacted quickly and killed both of them.

The Taliban swiftly claimed responsibility for the attack, with spokesman Zabihullah Mujahid saying the suicide bomber had inflicted heavy losses on police in Mazar-i-Sharif.

Two policemen were killed in attack, a police spokesman said, while a further 18 were injured according to the public health chief in Balkh province.

The attack followed a similar assault a day earlier in southern Helmand province, where a police officer was killed and others injured by a suicide bomber at the police headquarters in Lashkar Gar.

Elsewhere in Afghanistan, six people including three soldiers were killed when a suicide bomber detonated his car loaded with explosives near a convoy in central Wardak province, the governor s office said in a statement.

Eight others were also wounded in the attack, which took place in Sayedabad district.